Experimental and CFD Simulation Studies of Circulating Fluidized Bed Riser in the Fast Fluidization Regime

Hydrodynamics of gas-solid in the fast fluidization regime were investigated by a combination of experiment and computational fluid dynamics (CFD) simulations. A two-dimensional (2D) numerical simulation of gas-solids flow in a circulating fluidized bed riser was performed based on the two-fluid model (TFM). The effect of some essential parameters, namely, specularity coefficient (ϕ), and particle-particle restitution coefficient (e_ss), was examined for one set of operating condition. A range of specularity coefficients from 0.1 to 0.0001 were investigated. When specularity coefficient is set to values of 0.001 and above gives axial solid holdup profiles that reasonably agree with the experimental data. It was found that the specularity coefficient has substantial effect on bulk flow. Moreover, the effect of the elasticity of particle collisions showed that the high particle-particle restitution coefficients gave good quantitative agreement. Further extensive validations were carried out to investigate the validity of screened model parameters for different solid circulation rate and gas velocity. Simulation results for different operating condition were able to predict the qualitative trend. Although the model under-predicted the solid holdup at a high solid circulation rate, but was able to capture axial heterogeneity. The 2D results presented in this work will provide a useful basis for the future 3D simulation work of a current CFB system.